Inositol

What are myo- and D-chiro-inositol and what do they do in the body?

Inositol is a family of compounds with many isomers, such as myo-inositol (MI) and D-chiro-inositol (DCI). According to the review by Croze and Soulage, MI and DCI have been shown to have insulin-like properties and to be effective in lowering postprandial blood sugar. Abnormalities in inositol metabolism are associated with insulin resistance and with long-term microvascular complications of diabetes. The review states that MI is the most common inositol isomer in foods, and that it focuses on the possible benefits of MI supplementation in conditions associated with insulin resistance (PCOS, gestational diabetes, metabolic syndrome) and in some diabetes complications, which are based on clinical and/or animal studies. It has also been suggested that inositol glycans may be a second messenger of insulin. ^[8]

That a substance is related to the insulin pathway does not make it a necessary supplement for everyone. The sections below give each claim with its own study.

What is PCOS and what does the guideline say about inositol?

Polycystic ovary syndrome (PCOS) is the endocrinopathy that most commonly affects women of reproductive age; in the guideline process its prevalence was given as 10–13% (worldwide, using the Rotterdam criteria, according to the guideline’s ethnicity section). ^[1] The 2023 international evidence-based PCOS guideline (recommendations summarized by ASRM) recommends combined oral contraceptives as first-line pharmacological treatment for menstrual irregularity and hyperandrogenism, and metformin mainly for metabolic features, and states that metformin is more effective than inositol and that inositol offers limited clinical benefit in PCOS. The preferred first-line pharmacological treatment for infertility is letrozole. ^[1]

The guideline’s recommendations on inositol are as follows: (4.7.1) Inositol in any form could be considered according to individual preferences and values, noting limited harm and the potential for improvement in metabolic measures, but limited clinical benefit, including for ovulation, hirsutism, and weight (“could be considered”). (4.7.2) Metformin should be considered in preference to inositol for hirsutism and central adiposity (“should be considered”); the guideline notes that the gastrointestinal side effects of metformin are greater than those of inositol. For both recommendations, the certainty-of-evidence symbol is “very low” (⨁◯◯◯). (4.7.3) Women using inositol and other complementary therapies are encouraged to inform their health professional. (4.7.4) A specific inositol type, dose, or combination cannot currently be recommended in adults and adolescents because of a lack of quality evidence. (4.7.5) In the shared decision-making discussion, it is stated that the regulatory status and quality control of inositol (like other nutritional supplements) may differ from those of pharmacological products, and that dose and quality may vary. ^[1]

Does inositol work in PCOS?

The systematic review and meta-analysis by Fitz and colleagues, which underpins the 2023 guideline, covers 30 studies (2,230 people; 1,093 intervention, 1,137 control) examining the efficacy of inositol, alone or with other treatments, in PCOS management; 19 studies were included in the meta-analyses. Thirteen comparisons were evaluated, three of which entered meta-analysis. The findings show a benefit in some metabolic measures for myo-inositol or D-chiro-inositol, a possible benefit in ovulation for D-chiro-inositol, and possibly no effect in other outcomes. Compared with inositol, metformin may improve waist-to-hip ratio and hirsutism; there may be no difference in reproductive outcomes; evidence for body mass index is very uncertain. Myo-inositol probably causes fewer gastrointestinal side effects than metformin, but these are generally mild and self-limiting. The authors conclude that the evidence supporting inositol in PCOS management is limited and inconclusive. ^[2] The correction published for the article relates only to an error in the reference list. ^[3]

For this reason, the row for some metabolic measures in PCOS is at grade C, and the row for clinical outcomes such as ovulation, hirsutism, and weight is at grade D: the guideline finds harm limited and clinical benefit limited and uncertain; treatments such as metformin and combined oral contraceptives take first place in the guideline. ^{[1] [2]}

Is inositol use for fertility in PCOS evidence-based?

According to the guideline’s infertility section, (5.8.1) inositol, in any form, alone or with other treatments, should be considered an experimental treatment in infertile women with PCOS; the benefits and risks are too uncertain to recommend it as a fertility treatment (certainty of evidence ⨁◯◯◯). The effect on ovulation, clinical pregnancy, and live birth rests on limited and uncertain evidence (5.8.2); the side effects and safety of inositol are unknown (5.8.3); it is stated that these agents are subject to limited regulation and may vary in dose, quality, consistency, and combination with other agents (5.8.4). ^[1]

The 2018 Cochrane review (search July 2018) evaluated 13 studies including 1,472 subfertile women with PCOS (myo-inositol before IVF in 11 and during ovulation induction in 2); the evidence was of “low” to “very low” quality. In women undergoing IVF, the benefit of MI for live birth compared with standard treatment was uncertain (OR 2.42; 95% CI 0.75–7.83; 2 RCTs, 84 women; I² 0%). A reduction in the miscarriage rate (OR 0.40; 95% CI 0.19–0.86; 4 RCTs, 535 women; I² 66%) was reported with very-low-quality evidence, but this result rested mainly on a single study that reported an unusually high miscarriage rate in the control group; when this study was removed, the effect disappeared. There was no difference in multiple pregnancy rate (OR 1.04; 95% CI 0.63–1.71; 2 RCTs, 425 women). ^[4] For this reason, the row is rated E: no benefit has been shown for live birth.

Does inositol prevent gestational diabetes?

The meta-analysis by Poyatos-León and colleagues pooled 12 RCTs (4,765 women) comparing myo-inositol with placebo or standard care in women without diabetes who were pregnant or planning pregnancy within six months; most studies were of moderate to high quality, with some concerns about bias. Myo-inositol reduced the risk of gestational diabetes by 44% compared with control groups (no confidence interval is given in the abstract). No significant difference was found in secondary outcomes such as hypertensive disorders, cesarean section, macrosomia, preterm birth, and neonatal hypoglycemia. ^[5]

A clinical perspective article published on the same topic notes that there is substantial heterogeneity between studies in the primary outcome, which makes interpretation difficult. The article relays that the studies showed important differences in population characteristics (family history of diabetes, previous gestational diabetes, overweight/obesity), timing of treatment start (before or after week 14), and supplementation protocols; that study-level analyses could not separate true differences in effect from statistical power or other characteristics; that short-term tolerability was consistently reported, whereas long-term neonatal outcomes were rarely reported and safety data remained limited. The article concludes that the most suitable target group, protocol, and start time cannot be determined from the evidence. ^[6] The authors’ reported affiliations include an expert group named EGOI-PCOS that focuses on inositol research. ^[6] For this reason, the row is at grade C.

Does inositol work for depression and anxiety?

The 2014 meta-analysis by Mukai and colleagues (search through August 2013) pooled 7 double-blind placebo-controlled RCTs in depression (242 people; two bipolar depression, one bipolar depression and major depression, two major depression, two premenstrual dysphoric disorder) and 4 RCTs in anxiety disorders (70 people; two obsessive-compulsive disorder, one panic disorder, one PTSD). No statistically significant effect was found on depressive, anxiety, and obsessive-compulsive symptoms or on dropout rates; responders in depression were borderline more frequent than with placebo (p=0.06), a trend toward superiority in depressive symptoms in premenstrual dysphoric disorder (p=0.07) and a borderline increase in gastrointestinal discomfort (p=0.06) were reported. The authors state that the results suggest inositol may be useful particularly in depressed patients with PMDD, and that the main limitation is the small number of studies. ^[7] Because no significant effect was found, the row is rated E.

What is said about safety and quality?

The PCOS guideline associates inositol with limited harm (4.7.1) but states in the infertility section that side effects and safety are unknown (5.8.3). ^[1] In the meta-analysis by Fitz and colleagues, myo-inositol was reported to probably cause fewer gastrointestinal side effects than metformin, and these were generally mild and self-limiting. ^[2] In the Mukai meta-analysis, gastrointestinal discomfort was borderline more frequent than with placebo (p=0.06). ^[7] In pregnancy, short-term tolerability has been consistently reported and long-term neonatal outcomes rarely reported. ^[6]

The guideline states that the regulatory status and quality control of inositol (like other nutritional supplements) may differ from those of pharmacological products, and that dose and quality may vary; it cannot recommend a specific type, dose, and combination in adults and adolescents. ^[1] For this reason, the inositol type and amount on the label cannot be assumed to be comparable between products.

How are inositol supplements regulated in Türkiye?

In Türkiye, Ministry of Agriculture and Forestry approval is mandatory for every food supplement to be placed on the market; approval applications for imported products can be made only to the Istanbul and Ankara Provincial Directorates. ^[10]

In the latest update of the Ministry’s Restricted Substances List for food supplements (September 21, 2026), there is a row “Inositol (Inositol / Myo-inositol / D-Chiro-inositol) (together or alone)”. Sources: carob (Ceratonia siliqua), wheat, soybean, corn, and chemical synthesis. In the daily intake columns, at most 1,000 mg/day is written for ages 4–10 and at most 2,000 mg/day for ages 11 and older; the publication dates are March 8, 2016 for ages 11 and older and May 2, 2016 for ages 4–10, and the update date is June 27, 2016. The list also has “Phospholipids” (including phosphatidylcholine/lecithin and phosphatidylinositol) as a separate row; in this row the numerical limit columns contain a dash instead of a figure. ^[9] The limits in the list are daily intake columns; they are not related to any dose recommendation of the PCOS guideline.

Evidence table: claim, population, and limits

This guide does not recommend individual doses. For PCOS, pregnancy planning, current medications, and infertility treatment, the decision depends on individual assessment.